1. Field of the Invention
This invention constitutes a means and method for the excision of tissue from within the lumen of a human blood vessel by the use of a Precision Atherectomy Catheter (PAC) system. Although much of the description herein concerns atherectomy of plaque from within an artery, this invention is more generally applicable to the excision of any tissue from any blood vessel of a human body.
2. Description of the Prior Art
There are numerous treatments to remove tissue from lumens within the vessels in a human body including surgical interventions such as endarterectomy and by-pass surgery using veins or artificial graft materials. Balloon angioplasty is becoming increasingly popular for the dilation of arterial stenoses without the excision of the plaque. More recently atherectomy, the excision from an artery of atheromatous plaque, has been successfully used to open arterial stenoses.
In UK Patent Application GB-A 2,044,103 by D. N. Ross dated Oct. 15, 1980 there is described a device for removing plaque within an artery by drawing together two cutting edges that are initially placed on either side of an arterial stenosis. One significant disadvantage of the Ross invention is that it cannot cut a passageway through the plaque that is larger than the outside diameter of the catheter.
U.S Pat. No. 4,765,332, issued Aug. 23, 1988 to Robert E. and Tim A. Fischell, entitled "Pullback Atherectomy Catheter System," teaches a retrograde cutting catheter that can be advanced over a guide wire with a single cutting edge that can be rotated or mechanically vibrated, but does not teach a means for forming a passageway through the plaque that is larger than the outside diameter of the catheter.
U.S. patent application Ser. No. 447,187 filed on Dec. 7, 1989 by Robert E, Fischell and Tim A. Fischell (which is included herein by reference) describes an atherectomy catheter which also is incapable of forming a passageway though a blood vessel that is larger than the outside diameter of that catheter.
The European Patent Application No.EP-A 0 163,502 filed on May 5, 1985 by J. B. Simpson describes an atherectomy catheter which can form a passageway through an arterial stenosis that is larger than the outside diameter of the catheter. This is accomplished by inflating a balloon opposite a window in a housing at the catheter's distal end and pushing a cutter through the plaque and then pushing the plaque forward into a plaque collection chamber. The window is then rotated to a new position in the plaque and the process is repeated several times until a passageway is formed that is a larger diameter than the catheter's outer diameter when the balloon is not inflated. Although the Simpson invention does solve the problem of opening a passageway in the artery that is larger than the outside diameter of the catheter when the balloon in not inflated, there is no control over the thickness of plaque that is removed with each pass of the cutter. Thus at a low pressure in the balloon very little plaque would enter the window and therefore very little plaque would be removed. At a very high balloon pressure, much more plaque would be pushed into the window and therefore there would be a much deeper cut into the plaque and considerably more plaque would be removed (as compared to low pressure) and in fact the arterial wall could be (and in practice has been) perforated. Furthermore, for the same balloon pressures, harder plaque would not enter the window as much as softer plaque, and in that case, less plaque would be removed by the cutter. In summary, with the Simpson atherectomy catheter, the amount of plaque removed on each forward thrust of the cutter is indeterminate and arterial perforation does occur.